Detailed Render of the Earth from Space - Blender 2.5 - page 237

21. Let's start by duplicaing an exising Render Layers node and moving it to be
right below the controlledGlow3 node group.
22. Add a Mix node ( Add → Color → Mix ), set its mode to Add , its Fac to 2.0 , and
connect the image output of the controlledGlow2 node group to the top image
input. Then connect the image output of the controlledGlow1 output to the
botom image input.
23. Next, let's add two more Mix nodes; set the first to Additive mode and its Fac
to 5.0 . Then connect the image output of the controlledGlow3 node group to
the botom image input and the image output of the Render Layers node to the
top image input. For the other Mix node, set its mode to Add , its Fac to 0.5 , and
connect the image output of the Render Layers node to the top image input and
the image output of the mix node with a Fac of 2.0 to the botom image input.